Swift: Add CFG test cases for #available.

swift/ql/test/library-tests/controlflow/graph/Cfg.expected

@@ -6325,3 +6325,26 @@ cfg.swift:
 
 #  493| 13
 #-----|  -> exit testIfConfig() (normal)
+
+#  496| enter testAvailable()
+#-----|  -> testAvailable()
+
+#  496| testAvailable()
+#-----|  -> x
+
+#  497| var ... = ...
+#-----|  -> x
+
+#  497| x
+#-----|  -> if ... then { ... }
+
+#  497| x
+#-----| match -> 0
+
+#  497| 0
+#-----|  -> var ... = ...
+
+#  499| if ... then { ... }
+#-----|  -> StmtCondition
+
+#  499| StmtCondition

swift/ql/test/library-tests/controlflow/graph/cfg.swift

@@ -492,3 +492,29 @@ func testIfConfig() {
 
   13
 }
+
+func testAvailable() -> Int {
+  var x = 0;
+
+  if #available(macOS 10, *) {
+    x += 1
+  }
+
+  if #available(macOS 10.13, *) {
+    x += 1
+  }
+
+  if #unavailable(iOS 10, watchOS 10, macOS 10) {
+    x += 1
+  }
+
+  guard #available(macOS 12, *) else {
+    x += 1
+  }
+
+  if #available(macOS 12, *), #available(iOS 12, *) {
+    x += 1
+  }
+
+  return x
+}